Trio of Pacific typhoons intensify, creep closer to China and Japan

A trio of intensifying tropical cyclones is inching closer to China, Taiwan and southwest Japan as of Wednesday afternoon, eastern time. These storms — the strongest of which, Typhoon Nangka, is on the cusp of super typhoon status — are spinning toward southeast Asia, with at least one of them also raising concerns on the Japanese island of Okinawa.

The trio of tropical trouble was forecast by computer models a week in advance, though the same models are having trouble anticipating shifts in each storm's track and intensity.

The name, Chan-hom, comes from a tree that is found in Laos, among other countries.

Still, Chan-hom is a formidable storm that is the equivalent of a Category 3 hurricane. It is forecast to pass near the island of Okinawa on Thursday night or early Friday, local time. It may then pass well to the north of Taiwan on Friday night, before making landfall in China, near the city of Wenzhou in Zhejiang province on Saturday.

Depending how strong Chan-hom is when it makes landfall, and the exact track it takes, the storm could pose a significant flooding threat to both Wenzhou and Shanghai, a massive coastal city of about 14 million. Most of Shanghai is located at less than 10 feet above sea level, making it susceptible to storm-surge flooding, as well as flooding from heavy rainfall events.

The Joint Typhoon Warning Center (JTWC), run by the U.S. Navy and Air Force, is forecasting Chan-hom to make landfall as a 100-mile-per-hour storm, which is the equivalent of an intense Category 1 storm.

Chan-hom will then loop northeast, following the upper air flow over the region, which will be blowing from southwest to northeast. Exactly where the northeast turn begins will help determine the extent of storm impacts in Shanghai in particular; a track to the west or over the city would bring more rain and wind, compared to a track to the east of the city.

The JTWC said it has "low confidence" in the long-range forecast track due to uncertainty of where the northeast turn takes place.

The recurving typhoon, together with the storm behind it — Typhoon Nangka — may help energize the jet stream across the North Pacific, reconfiguring weather patterns as far away as Alaska, Canada and the United States about one to two weeks later.

Chan-hom, Nangka and Linfa line the NW Pac. Last time that the NW Pac had 3 TCs at 55 kt+ strength was on 9/8/00. pic.twitter.com/ES1EQ01qom

Typhoon Nangka

Following close behind Typhoon Chan-hom is Typhoon Nangka, which as of Wednesday at 2 p.m. ET was a 130-mile-per-hour storm; that makes it the equivalent of a Category 4 storm. It may continue intensifying during the next 24 hours, possibly peaking at super typhoon intensity, as forecast by the JTWC.

Typhoon Nangka could be a long-range threat to Japan, according to these computer model projections.

Image: WeatherBELL Analytics

The storm is benefiting from the position and influence of a tropical upper tropospheric trough, known by the meteorological acronym "TUTT;" this helps evacuate air from the northern part of the typhoon. Enhancing the outflow of air at upper levels of the atmosphere helps tropical cyclones grow, since they are sucking in so much air from the lower atmosphere, converting it to energy, and vaulting it to high heights.

A lack of adequate outflow can often stymie such storms.

After that, the storm is forecast to move more north than west, while also weakening.

Typhoon Nangka does not appear to be a threat to China or Taiwan, but it may threaten parts of Japan early next week.

Typhoon Linfa

Typhoon Linfa, for example, intensified to near-typhoon status unexpectedly, with sustained winds of at least 70 miles per hour, as it made its way on a distinctive track to the southwest, making landfall late Wednesday EDT between 100 to 200 miles northeast of Hong Kong.

It further intensified to a typhoon as it formed a clear eye on satellite imagery, a telltale sign of a strong tropical cyclone.

The storm, which is small enough that it could fit within Typhoon Chan-hom's cloud field multiple times over, is expected to weaken while producing heavy rainfall across Hong Kong, before delivering a glancing, squally blow to Hainan Island, and then looping back out to sea, where it may get absorbed by the seasonal monsoon in that region.

Why the surge in storms?

The burst of storm activity has to do with two main factors: a strengthening El Niño event and the Madden-Julian Oscillation.

The El Niño event is bringing much above average ocean temperatures to a broad area of the tropical Pacific Ocean, roughly from the international dateline eastward to South America, though there are some areas of above average water temperatures all the way west toward the Philippines.

The sudden burst of activity in the central and western Pacific Ocean follows a six-week lull in activity there, after this part of the world had its most active start to the typhoon season on record. Three of the first four typhoons that developed reached the equivalent of a Category 5 hurricane, and the planet has already seen as many Category 5 storms as it typically does in a given year.

El Niño events tend to increase the amount of storminess in areas just north and south of the equator, and these tropical thunderstorms, if given the right encouragement from the atmosphere, can start to organize, take on some rotation and intensify into a fledgling tropical cyclone.

Interestingly, the feedbacks between El Niño and tropical cyclones goes both ways, as such storms can help to intensify or maintain El Niño conditions. In the current instance, the trio of storms is helping to propel a westerly wind burst across the equator, traveling like a row of dominoes lined up from west to east along the equator. This wind burst has actually reversed the typical trade winds in some areas.

Instead of blowing from east-to-west, as they usual do, the winds are blowing from west-to-east, helping to propel a pulse of mild water eastward and intensify the El Niño.

The N. Pacific jet stream winds will blow stronger after the typhoons curve out to sea, causing a shift in downstream weather patterns.

Image: WeatherBELL Analytics

The other factor at work is a global weather cycle known as the Madden-Julian Oscillation, or MJO. Named after meteorologists Roland Madden and Paul Julian, who first described the cycle in 1971, the MJO is an eastward-moving disturbance of clouds, rainfall, winds and pressure that circles the globe in about 30 to 60 days, according to the National Oceanic and Atmospheric Administration (NOAA).

The MJO has two phases, an enhanced rainfall phase and a suppressed rainfall phase. Recently, the central and western Pacific entered into a particularly strong enhanced rainfall phase, after being in a six-week suppressed phase.

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